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Inability of purified Pseudomonas aeruginosa exopolysaccharide to bind selected antibiotics
Abstract:
It has been proposed that the exopolysaccharide (alginate) of mucoid Pseudomonas aeruginosa strains which infect cystic fibrosis patients might bind and hence protect this pathogen from antibiotics. To test this hypothesis, we employed equilibrium dialysis to measure the binding between several antibiotics and purified Pseudomonas alginate. Binding was calculated from the residual concentrations of antibiotics in free solution by a biological assay. The detectable binding of antibiotics to alginate was consistent with expectations; the positively charged antibiotics steptomycin and tobramycin, bound to the polyanion (0.047 and 0.024 mumol/mg of alginate, respectively), whereas the neutral species, clindamycin and penicillin, bound negligibly or not at all (0.0011 and 0 mumol/mg of alginate, respectively). When these experiments were performed in the presence of physiological concentrations of saline, none of the antibiotics bound to the polysaccharide. Since the binding observed was abrogated by salt concentrations typical of the tracheobronchial secretions of cystic fibrosis patients, the data suggest that tight binding of antibiotics to the exopolysaccharide of a mucoid P. aeruginosa strain does not provide increased antibiotic resistance.
Insights
Antibiotic binding to Pseudomonas aeruginosa alginate, a component of cystic fibrosis infections, was investigated. Positively charged antibiotics showed some binding, but this interaction was eliminated by salt, suggesting alginate does not confer significant antibiotic resistance.
Area of Science:
- Microbiology
- Pharmacology
- Biochemistry
Background:
- Mucoid Pseudomonas aeruginosa is a major pathogen in cystic fibrosis patients.
- The exopolysaccharide alginate produced by these bacteria may protect them from antibiotics.
- Understanding this interaction is crucial for developing effective cystic fibrosis treatments.
Purpose of the Study:
- To determine if Pseudomonas aeruginosa alginate binds to antibiotics.
- To assess whether alginate binding contributes to antibiotic resistance in cystic fibrosis infections.
- To quantify the binding affinity between alginate and various antibiotics.
Main Methods:
- Equilibrium dialysis was used to measure antibiotic binding to purified Pseudomonas alginate.
- Binding was quantified by measuring residual antibiotic concentrations using a biological assay.
- Experiments were conducted with and without physiological saline concentrations.
Main Results:
- Positively charged antibiotics (streptomycin, tobramycin) exhibited measurable binding to alginate.
- Neutral antibiotics (clindamycin, penicillin) showed negligible or no binding.
- The observed binding was completely abrogated in the presence of physiological saline concentrations.
Conclusions:
- Antibiotic binding to Pseudomonas aeruginosa alginate is minimal and dependent on charge.
- Salt concentrations found in cystic fibrosis patient secretions abolish alginate-antibiotic binding.
- Alginate does not appear to provide significant antibiotic resistance to mucoid Pseudomonas aeruginosa in vivo.